Experimental Study On Pool Fire Environment In Ship Room With Ceiling Vent

As a typical compartment fire, the fire occurring in ship engine room with ceiling vent has resulted in the greatest number of fire fatalities due to the abundance of ignition sources in close proximity with flammable liquids. Compartment fire with vertical wall vents or horizontal ceiling vents might have different behaviors, because the flow exchange at the openings and vents is of considerable importance in the compartment fire growth and spread. It is therefore very important that carrying on the research on the fire development in the compartment with ceiling vent, to gain the knowledge of how the fire grows in such compartment at different ventilation conditions and how to control the fire spread and rescue.Experimental studies were carried out in a compartment with dimensions of 100cm (length)×100cm (width)×75cm (height). Rectangular openings with various sizes from 25 cm2 (5cm×5cm) to 900 cm2 (30cm×30cm) were located at one corner of the ceiling. Heptane pool fires with diameter of 10cm, 14cm and 20cm were adapted as fire source. In present study, the effects of opening size on the pool fire behavior were studied. Furthermore, the filling process of smoke in the enclosure together with the exchange flow at the ceiling opening is investigated. Then, detailed analysis of the heat transfer mode in compartment fires with ceiling openings is conducted to understand the heat distribution in the fire and finally establish the fire dynamic model for enclosure fires with ceiling openings. The detailed work is as follows:The effect of ceiling vent size on the burning behavior of pool fire. Two kinds of burning are decided according to the reason for fire extinction as“oxygen-lack”mode and“fuel exhaust”mode. When under the“oxygen-lack”mode, flame would change from steady burning state to an unsteady state in which flame wonders around the fuel surface. The fire plume entrains contaminated gas with decreasing oxygen concentration and the effects of the opening sizes on fuel mass loss rate are rare. When under the“fuel exhaust”mode, flame keeps in steady burning state, the oxygen concentration in the entrained gas stays at a relatively unchanged value after the initial decreasing stage, and the fuel mass loss rate increases dramatically due to the boiling of the fuel. According to the oxygen consumption, the combustion efficiency decreases with the increasing of pool diameter for a given compartment.The filling process of smoke in compartment fire with ceiling vent. By comparison, it can be observed that the determination method of layer interface based on the temperature stratification can be adapted in enclosure fires with ceiling openings. Smoke layer quickly descends to the enclosure floor, so“single zone”model is proper for both“oxygen-lack”and“fuel exhaust”conditions. Based on the main assumption of“single zone”model, a prediction model for gas temperature in enclosure fires with ceiling openings is established. As the burning continues, the heat loss fraction should increase accordingly to get a good prediction. This indicates that more heat from the fire is converted from the walls to the outside environment and used to heat the walls.The basic nature of the gas flow through the horizontal ceiling vent in the compartment fire. The flow patterns across the ceiling vent are observed to study the basic characteristics of the flow resulting from the imposed pressure and temperature across the vent by use of the laser sheet arrangement. Under the small veiling vent condition, the downward flow decreases to zero, a unidirectional upward flow is found at the vent. As the vent size increases, the flow is bidirectional, the ambient air descends in the compartment and the smoke rises up across the vent. The calculating results show that when the thermal expansion pressure is larger than the critical pressure, the flow is unidirectional and the flow rate is determinated by the thermal expansion; when the pressure is smaller than the critical pressure, a bidirectional symmetric flow across the vent is observed, with the mass flow is taken as the pressure-and buoyancy-driven; for a zero pressure difference, the pressure-driven flow drop to zero and the two-way flow rate are only determinated by the buoyance-driven. The mass flow rates across the ceiling vent are given. The inflowing and out flowing mass rates increase as ceiling vent increases, and under much larger vent size, the effect of thermal expansion pressure can be ignored, the fresh air flow rate is larger than that of smoke.The heat transfer mode in ceiling vent compartment fire and predicting model of fire dynamic parameters. We analyse the heat transfer including convection, radiation and conduction among the flame, gases and the compartment. Based upon the heat conservation equation, we found that most of the heat release from the fire was lost to the ceiling and walls, only approximately 10% of the total heat generated by combustion heated the gases and leaked from the ceiling vent. With the burning of the fuel, the heat loss coefficient became larger and larger and maintained within 0.9~1 at the late stage of the fire. In addition, a model for predicting the temperature, oxygen concentration and pressure in a compartment with a ceiling vent was proposed based upon the one zone assumption and the conservation equations of mass, energy and components. The change tendency and the value of the predicted and the experimental results show a good agreement.